I am working on 4-layer PCB with following stack-up:
- Layer-1 Signal traces
- Layer-2 Ground
- Layer-3 Ground
- Layer-4 Signal + Power traces
The PCB contains ESP32-S2 MCU with USB and chip antenna. I am going to use JLC PCB for manufacturing with this impedance controlled stack-up (1 mm PCB thickness).
I have calculated required trace width to get 50 ohm impedance for RF trace and 90 ohm diff. impedance for USB lines.
According to the hardware guidelines provided by Espressif Systems, It requires unbroken ground plane under both these impedance controlled traces. I have Unbroken ground planes in layer 2 and layer 3, but not in layer 4.
Is it okay to have signal or power traces under impedance controlled traces in layer 4 as shown in both these images below? (Check red marked area in layer 4)